This project is an attempt to further define the role of the nude, athymic mouse as a model for various human disease processes. Initial exposure to the nude mice with human hepatitis A and B virus was unsuccessful. They did, however, demonstrate the role of the cellular immune response in lesions of schistosomiasis. The use of antilymphocyte serum and the breeding of the nude as a congeneic with inbred strains of mice lacking specific immune responses will be continued in an effort to provide a new model for human infectious diseases.